Embolus blood clot filter with floating filter basket

ABSTRACT

A blood filter device for placement in a blood vessel including a plurality of anchor members disposed radially and extending angularly about a first hub. A filter basket is preferably positioned upstream from the anchor members. The anchor members each include a hook configured to penetrate the vessel wall to prevent longitudinal movement due to blood flow. The filter basket is made up of a number of filter members configured to retain blood clots within the basket without completely blocking blood flow or applying additional force to vessel walls. Portions of the filter members may project radially outward to position the basket near the vessel centerline, but the filter basket preferably does not include hooks or anchors for anchoring the filter basket to the blood vessel.

PRIORITY DATA AND INCORPORATION BY REFERENCE

This application claims benefit of priority to U.S. Provisional PatentApplication No. 60/754,599, filed Dec. 30, 2005 which is incorporated byreference in its entirety. This invention is related to the subjectmatter shown and described in the following: (i) PCT Internationalapplication Ser. No. ______, filed Dec. 29, 2006, having Attorney DocketNo. 14673-007WO, entitled “Removable Blood Clot Filter with Edge ForCutting Through the Endothelium” and claiming the benefit of priority toU.S. Provisional Patent Application No. 60/754,600, filed Dec. 30, 2005;(ii) PCT International application Ser. No. ______, filed Dec. 29, 2006,having Attorney Docket No. 14673-004WO, entitled “Embolus Blood ClotFilter with Post Delivery Actuation,” and claiming the benefit ofpriority to U.S. Provisional Patent Application No. 60/754,633, filedDec. 30, 2005; (iii) PCT International application Ser. No. ______,filed Dec. 29, 2006, having Attorney Docket No. 14673-008WO, entitled“Embolus Blood Clot Filter Delivery System,” and claiming the benefit ofpriority to U.S. Provisional Patent Application No. 60/754,636, filedDec. 30, 2005; (iv) PCT International application Ser. No. ______, filedDec. 29, 2006, having Attorney Docket No. 14673-011 WO, entitled“Embolus Blood Clot Filter Removal System and Method,” and claiming thebenefit of priority to U.S. Provisional Patent Application No.60/754,598, filed Dec. 30, 2005; and (v) PCT International applicationSer. No. ______, filed Dec. 29, 2006, having Attorney Docket No.14673-010WO, entitled “Embolus Blood Clot Filter with Bio-ResorbableCoated Filter Members,” and claiming the benefit of priority to U.S.Provisional Patent Application No. 60/754,597, entitled “Embolus BloodClot Filter with Retainers on Locator Filter Members,” filed Dec. 30,2005, each of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to a filter device that can be placed in a bloodvessel to reduce the risk of embolisms and, more particularly to afilter that will not increase pressure applied to the blood vessel wallsas emboli are captured from the blood.

BACKGROUND ART

In recent years, a number of medical devices have been designed whichare adapted for compression into a small size to facilitate introductioninto a vascular passageway and which are subsequently expandable intocontact with the walls of the passageway. These devices, among others,include blood clot filters which expand and are held in position byengagement with the inner wall of a vein, such as the vena cava. Suchfilters include structure to anchor the filter in place within the venacava, such as elongate diverging anchor members with hooked ends thatpenetrate the vessel wall and positively prevent longitudinal migrationof the filter within the vessel.

A number of conditions and medical procedures subject the patient to ashort term risk of pulmonary embolism which can be alleviated by afilter implant. In such cases, the filter catches and retains emboli toprevent them from reaching the lungs or the brain. A number ofconfigurations of blood filters are known. An example of such a filteris disclosed in U.S. Pat. No. 6,258,026 and illustrated in FIGS. 16 and17.

Typical previously known blood filters include a number of locatormembers 20 and anchor members 30. The locator members 20 and anchormembers 30 may be offset one from the other about the longitudinal axisof the filter 1, as shown in FIG. 17. Hooks 40 positioned on the distalends of the anchor members 30 engage the blood vessel wall to preventlongitudinal movement within a blood vessel. When in place in a bloodvessel 6, anchor members 30 form a first filtering zone 10 and locatormembers 20 form a second filter zone 11, as shown in FIG. 18.

First filtering zone 10, which is defined by anchor members 30, receivesblood flow 8 before blood reaches the remainder of the filter 1. Soemboli 5 tend to be captured preferentially in first filtering zone 10,as illustrated in FIG. 18. This result has disadvantages when asignificant mass of emboli 5 are retained. For one, under the pressureof blood flow 8, the emboli 5 will press with a force F₀ against anchormember 30 which results in a radial force component F₂. Acting as alever, anchor member 30 translates the radial force component F₂ intogreater stress 100 applied to the blood vessel walls 6 by the hooks 40.Over time, the stress 100 applied to the vessel walls 6 may lead tovascular injury or disease. In addition, since the anchor members 30must engage the vessel wall to hold the filter 1 in place, the firstfiltering zone 10 is susceptible to complete filling such that emboli 5span the entire cross section of the blood vessel, as illustrated inFIG. 19. If this happens, in addition to increasing the stress 100applied to the blood vessel wall 6, the captured emboli will completelyblock blood flow through the vessel.

Accordingly, there is a need for a blood filter which will not increasestress applied to blood vessel walls as emboli are captured and will notcompletely block blood flow if filled with emboli.

DISCLOSURE OF INVENTION

A preferred device provides for filtration of emboli in a blood vesselwithout the captured emboli causing increased stress on the blood vesselwalls or total blockage of blood flow.

In an embodiment, a blood filter includes first and second hubs, atleast one anchor, and a filter basket preferably configured not toanchor to the blood vessel wall. The first and second hubs may bedisposed along a longitudinal axis. Anchor members extend from the firsthub and engage the blood vessel wall with hooks to prevent longitudinalmovement of the filter. The second hub is coupled to the first hub, suchas by means of a connector (e.g., wire or bundle of wires). The filterbasket is made up of a number of filter members that are coupled to thesecond hub and project radially and longitudinally away from the secondhub. A retainer member limits radial expansion of the filter members. Inan embodiment, the retainer member is configured to project radially soas to position the open end of the filter basket within the bloodvessel. In an embodiment, the filter basket further includes two or moreretainer members separated by a distance along the longitudinal axis tofurther limit radial expansion of the filter members. Preferably, thefilter members and retainer members are made from a shape memory alloy,such as Nitinol.

In another embodiment, a blood filter includes first and second hubs, atleast one anchor, and a filter basket preferably configured not toanchor to the blood vessel wall.

The first and second hubs may be disposed along a longitudinal axis.Anchor members extend from the first hub and engage the blood vesselwall with hooks to prevent longitudinal movement of the filter. Thesecond hub is coupled to the first hub, such as by means of a wire orbundle of wires. The filter basket is made up of a number of filtermembers that are coupled to the second hub and project radially andlongitudinally away from the second hub.

A retainer member limits radial expansion of the filter members. Thefilter members may be configured to project radially at their distalends so as to position the open end of the filter basket within theblood vessel. In an embodiment, the filter basket further includes twoor more retainer members separated by a distance along the longitudinalaxis to further limit radial expansion of the filter members.

In another embodiment, a blood filter includes first and second hubs, atleast one anchor, and a filter basket preferably configured not toanchor to the blood vessel wall. The first and second hubs may bedisposed along a longitudinal axis. Anchor members extend from the firsthub and engage the blood vessel wall with hooks to prevent longitudinalmovement of the filter. The second hub is coupled to the first hub, suchas by means of a wire or bundle of wires. The filter basket is made upof at least one filter member that is coupled to the second hub andshaped in the form of a helix. If more than one helical filter member isincluded, the helical filter members are angularly offset about thelongitudinal axis. The filter members may include a distal portion whichprojects radially outward so as to position the open end of the filterbasket within the blood vessel.

In another embodiment, a blood filter includes a single hub, a pluralityof anchor members, and a filter basket preferably configured not toanchor to the blood vessel wall. The hub may be disposed along alongitudinal axis. Anchor members extend from the hub and engage theblood vessel wall with hooks to prevent longitudinal movement of thefilter. The filter basket is made up of a plurality of filter memberseach of which has a generally linear extended segment and a filterbasket segment. The extended segments of the filter members are coupledto the hub. The filter basket segments may form a rectilinear filterbasket, a birdcage-like filter basket or a helical filter basket. Aretainer member may be coupled to the filter basket segments, and thefilter members may further include a distal segment which projectsradially outward so as to position the open end of the filter baskedwithin the blood vessel.

In another embodiment, a blood filter includes first, second and thirdhubs, at least one anchor, and first and second filter baskets that arepreferably configured not to anchor to the blood vessel wall. The first,second and third hubs may be disposed along a longitudinal axis. Anchormembers extend from the first hub and engage the blood vessel wall withhooks to prevent longitudinal movement of the filter. The second hub iscoupled to the first hub, such as by means of a connector (e.g., wire orbundle of wires). The first filter basket is made up of a number offilter members that are coupled to the second hub and project radiallyand longitudinally away from the second hub. A retainer member limitsradial expansion of the first filter members. In an embodiment, theretainer member is configured to project radially so as to position theopen end of the first filter basket within the blood vessel. The thirdhub is coupled to the second hub, such as by means of a connector (e.g.,wire or bundle of wires). The second filter basket is made up of anumber of second filter members that are coupled to the third hub andproject radially and longitudinally away from the third hub. A secondretainer member limits radial expansion of the second filter members. Inan embodiment, the second retainer member is configured to projectradially so as to position the open end of the second filter basketwithin the blood vessel. Preferably, the filter members and retainermembers are made from a shape memory alloy, such as Nitinol.

The various embodiments provide a filter that includes a filteringbasket that is positioned upstream (with respect to blood flow throughthe vessel) from the filter's anchor members. The embodiments provide afilter that can remove emboli from the blood before they encounter thefilter's anchoring members. So positioned, the filter basket can besmaller in cross section than the blood vessel so a full filter does notclog the blood vessel. Also, the volume of the filter basket can becontrolled by lengthening the filter members so a larger volume ofemboli can be removed without leading to blockage of the blood vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate example embodiments of theinvention, and, together with the general description given above andthe detailed description given below, explain features of the invention.

FIG. 1 is a perspective view of a filter according to an embodiment.

FIG. 2 is a side view of the filter of FIG. 1 viewed along A-A.

FIG. 3A is an end view of the filter of FIG. 2 viewed along B-B.

FIG. 3B is a side view of the filter basket of the filter shown in FIG.2 viewed along C-C.

FIG. 4A is an end view of another embodiment of the filter basket.

FIG. 4B is a side view of the filter basket of FIG. 4A.

FIG. 5 is a detailed schematic view of a retainer member for the filterof FIG. 1 transforming from the configuration in FIG. 4B to theconfiguration of FIG. 6.

FIG. 6 is a side view of the filter basket of the filter shown in FIG. 1in a folded configuration.

FIG. 7 is a side perspective view of another embodiment of the filterbasket.

FIG. 8 is a side perspective view of yet another embodiment of thefilter basket.

FIG. 9 is a side view of the filter basket of FIG. 8 in a foldedconfiguration.

FIG. 10 is a side perspective view of another embodiment of the filterbasket.

FIG. 11 is a side view of the filter basket of FIG. 10.

FIG. 12A is a side perspective view of yet another embodiment of thefilter basket.

FIG. 12B is an end view of another embodiment of the filter.

FIG. 13 is a side perspective view of the filter basket of FIG. 12Adisposed in a blood vessel.

FIG. 14 is a side perspective view of another preferred embodiment ofthe filter.

FIG. 15 is a side perspective view of yet another embodiment of thefilter.

FIG. 15A is a side perspective view of another embodiment of the filter.

FIG. 16 is a perspective view of a known blood filter.

FIG. 17 is an end view of the filter shown in FIG. 16 implanted in ablood vessel.

FIG. 18 is a perspective view of the filter shown in FIG. 16 implantedin a blood vessel.

FIG. 19 is another perspective view of the filter shown in FIG. 16implanted in a blood vessel.

MODE(S) FOR CARRYING OUT THE INVENTION

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicate a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. Also, as used herein, the terms “patient”,“host” and “subject” refer to any human or animal subject and are notintended to limit the systems or methods to human use, although use ofthe subject invention in a human patient represents a preferredembodiment.

FIGS. 1-15A illustrate various embodiments of blood filters which filteremboli in a blood vessel of a subject such that the captured emboli tendnot to cause increased pressure on the blood vessel walls or totalblockage of blood flow. The preferred embodiments of the blood filterprovide a first filtering element or filter basket, upstream withrespect to the filter's anchor members. When appropriately located andoriented within a blood vessel, the filter basket is able to removeemboli from the blood before the emboli encounter the anchor members.The filter basket can be configured to have a smaller open face (i.e.,smaller cross section) than the blood vessel's cross section.Preferably, the filters define a filtering volume that can be adjustedto retain more emboli without changing the filter's anchor members.

Referring to FIG. 1, a preferred embodiment of the filter 1 isillustrated in a perspective view. This embodiment of a filter includesa first hub 12, anchor members 30 projecting from the first hub 12 eachhaving a hook 40, a second hub 14 connected to the first hub 12 by aconnector 13, and a filter basket 50 coupled to the second hub 14.Locators 20, which position the filter 1 in the center of the bloodvessel, may be coupled to the first hub 12 or provided as part of thefilter basket 50. These locators 20 are preferably a part of the filterbasket 50, as shown in FIG. 1.

The filter 1 may be made from any combination of suitable bio-compatiblematerials, such as, for example, polymer, memory polymer, memory metal,thermal memory material, metal, metal alloy, or ceramics. The anchormembers 30 and filter members 51, 52 and 56 can be made from a pluralityof elongate wires, which are preferably metal such as theCobalt-Chromium-Nickel alloy known as Elgiloy®, and more preferably asuper elastic shape memory alloy, such as Nitinol. The shape memoryalloy can further be defined as preferably having an austenite finish(Af) temperature below body temperature. Nitinol is a low modulusmaterial that allows the anchor and filter members of the filter 1 tohave low contact forces and pressures while still achieving sufficientanchoring strength to resist migration of the device within a bloodvessel. As used herein, “wire” refers to any elongated member of narrowcross section, including rods, bars, tubes, ribbon and narrow sectionscut from thin plate, and is not intended to limit the scope of theinvention to elongated members of circular cross section, cut from wirestock or manufactured according to a particular method of metal forming.Although the filters of the various embodiments are preferably formedfrom a temperature-responsive shape memory material, such as Nitinol,they can also be formed of a compressible spring metal such as stainlesssteel, Elgiloy®, or a suitable plastic.

Anchor members 30 have a proximal end coupled to the first hub 12 and adistal end formed into or coupled to a hook 40. The anchor members 30may be held together on their proximal ends at the first hub 12 by anyof a number of a suitable connection techniques, such as, for example,welding, laser welding, plasma welding or being bonded together. Thefirst hub 12 may be hollow or have an interior space into which theproximal ends of the anchor members 30 may be inserted prior to bonding,such as by brazing, welding (preferably plasma welding) or gluing with abiocompatible adhesive.

For illustration purposes only, FIGS. 1 and 2 show four anchor members30. But fewer or more anchor members 30 may be used. For example, aminimum of three anchors may be used to ensure that the filter 1 iscentered in the blood vessel. Alternatively, a filter 1 with six or moreanchor members 30 positions the anchor members close enough together forthem to function as a second filter basket.

Referring to FIG. 2, each of the plurality of anchor members 30preferably include a first anchor segment 31 connected via a bend to asecond anchor segment 32, which may be connected to a third anchorsegment 33 via another bend 34. In a preferred embodiment, the thirdanchor segment 33 is connected to a hook 40 or bent into a hook 40. Inother embodiments, the anchor members 30 may include fewer or moresegments.

As shown in FIG. 2, a portion of first anchor segment 31 is disposedwithin the hub 12 and may be welded, brazed or otherwise coupled toother anchor members within the first hub 12. First anchor segment 31preferably includes a first bend oblique with respect to thelongitudinal axis A, which provides the linkage between the first andsecond anchor segments. The second anchor segment 32 may extend alongaxis 130 oblique with respect to the axis A at an angle θ₁ with respectto the longitudinal axis A. The third anchor segment 33 extends alongaxis 140 oblique with respect to the longitudinal axis A at an angle θ₂.The second anchor segment 32 may have a length L₁ measured along axis130 from the first hub 12, and the third anchor segment 33 may have alength L₂ measured along axis 140 from bend 34. The thickness of anchormember 30 is nominally t₁. Where the anchor member 30 is a wire ofcircular cross section, the thickness t₁ of the anchor 30 may be thediameter of the wire. As shown in the detail in FIG. 2, the hook 40 maybe contiguous to a plane and characterized by a radius of curvature R₁.The hook 40 has a diameter or thickness t₂, which may be less than thethickness t₁ of the rest of the anchor member 30. The anchor members 30,in their expanded configuration illustrated in FIGS. 1 and 2 (i.e.,unconstrained in the high temperature form), are at a slight angle tothe blood vessel wall, preferably within a range of from ten toforty-five degrees, to present the hooks 40 in an orientation thatfacilitates penetrating the vessel wall in order to secure the filter 1within the vessel.

In another embodiment, the filter basket 50 can be configured to expandto an outer diameter greater than the inside diameter of a host bloodvessel and the connector 13 can be configured to facilitate detachinghub 12 from hub 14. Due to the larger size of the filter basket in thisembodiment, the filter basket would tend to be adhered to the vesselwall via tissue ingrowth, thereby allowing the anchor members 30 and hub12 to be removed from the blood vessel by disconnecting hub 12 from hub14 while leaving the filter basket permanently in place. Preferably, theconnector 13 can be configured as a bio-resorbable material or asuitable, detachable coupling means so that the connector 13 may bedisconnected from hub 14.

The aforementioned filter and anchor member dimensions may be adjustedto accommodate inserting, locating or positioning, and securing of thefilter 1 into blood vessels of varying diameters. The dimensions arepreferably selected so that, when placed in the vessel, the hooks 40press against the walls of the vein or vessel with sufficient radialforce to ensure that the hooks engage the wall but not so much force asto cause injury to the wall. For example, a filter intended to be placedin a narrow vein or vessel, such as a child or canine vena cava, mayhave smaller dimensions than a filter intended to be placed in a largevein or vessel, such as an adult vena cava or femoral vein.

In an exemplary filter embodiment suitable for an adult human vena cava,when the filter 1 is at the temperature of the subject andunconstrained, the length of the second anchor segment 32 may be about0.5 inches; the length of the third anchor segment 33 may be about 0.8inches; the first angle θ₁ may be about 20 degrees to about 90 degrees;the second angle θ₂ may be about 0 degrees to about 60 degrees; thethickness t₁ of the anchor member may be about 0.013 inches; thethickness t₂ of the hook 40 may be about half the thickness t₁ of theanchor member 30; and the hook may have a radius R₁ of about 0.030inches. In a preferred embodiment, the anchor member 30 has a crosssectional area of about 0.00013 squared inches, and the hook 40,particularly the curved section, has a cross sectional area of about0.000086 squared inches.

The size (i.e., radius and thickness) of the hooks 40 for migrationresistance, as well as the number of anchor members 30, may bedetermined by calculating the force applied to each hook when the filter1 is fully occluded and the blood pressure in the vessel is allowed toreach 50 millimeters of mercury (mmHg). This force is approximately atleast 70 grams on each anchor of a six-anchor device for at least 50mmHg pressure differential in a 28 mm vessel. The desired totalmigration resistance force for an adult human vena cava filter isbelieved to be approximately 420 grams, and the load on the filter 1would be correspondingly smaller in vessels of smaller diameter. Tolower the maximum migration force that must be resisted by each hook,additional anchor members 30 with hooks 40 can be added to the filter 1.

It is preferable that the hooks 40 perform as an anchoring mechanism ata predetermined filter migration resistance force preferably defined asa function of a blood pressure range in the vessel, which is furtherpreferably from about 10 mmHg up to about 150 mmHg. Having maintainedits geometry at a predetermined filter migration resistance force withinthis range, the hook 40 preferably begins to deform in response to ahigher force applied in the direction of the hubs, and releases at aforce substantially less than that which would cause damage to thevessel tissue. The ability of the hook 40 to straighten somewhat allowsthe filter to be safely removed from the vessel wall. The migrationforce can be derived determined from a given pressure value using thefollowing calculations, for example:

Since 51.76 mmHg=1.0 pounds per square inch (psi), 50 mmHg=0.9668 psi;Eq. 1.

For a 28 mm vena cava:

$\begin{matrix}{{{A = {{\frac{\pi}{4}(28)^{2}\mspace{14mu} {mm}^{2}} = {{615.4\mspace{14mu} {mm}^{2}} = {0.9539\mspace{14mu} {inches}^{2}}}}};}.} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

Migration force is calculated by:

$\begin{matrix}\begin{matrix}{P = \frac{F}{A}} & {{{F = {P \times A}};}.}\end{matrix} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

0.9668 psi×0.9539 inches^(2=0.9223) pounds=418.7 grams. Eq. 4.

Depending on the number of hooks 40, the required strength of each hookcan be calculated. For a device with six hooks:

$\begin{matrix}{{{Hook}\mspace{14mu} {Strength}} = \frac{{Filter}\mspace{14mu} {Migration}\mspace{14mu} {Resistance}\mspace{14mu} {Force}}{{Number}\mspace{14mu} {of}\mspace{14mu} {Hooks}}} & {{Eq}.\mspace{14mu} 5} \\{= {\frac{418.7}{6} = {69.7\mspace{14mu} {grams}}}} & {{Eq}.\mspace{14mu} 6}\end{matrix}$

So each hook must be capable of resisting approximately at least 70grams of force for the filter 1 to resist at least 50 mmHg pressuregradient in a 28 mm diameter vessel. In order to prevent or minimizeexcessive vessel trauma, each individual hook preferably has a low hookstrength. By balancing the number hooks 40 and the individual hookstrength, minimal vessel injury can be achieved while still maintainingthe at least 50 mmHg pressure gradient criteria, or some otherpredetermined pressure gradient criteria within a range of about 10 mmHgto 150 mmHg.

Positioned upstream with respect to blood flow 8 from the anchor members30 is a filter basket 50 oriented such that the basket opening facesaway from the anchor members 30. In the embodiment illustrated in FIG.1, the filter basket 50 is preferably coupled to a second hub 14 whichitself is coupled to the first hub 12 by a connector 13. It should benoted that the second hub 14 and connector 13 are included in some butnot all embodiments, and thus are optional elements.

The connector 13 connects the first and second hubs 12, 14 at aseparation distance L₃. The connector 13 is preferably strong and stiffenough to transmit compression force—such as may occur during filterdelivery and operation—from the second hub 14 to the first hub 12without buckling, and the connector 13 may also be flexible enough topermit the filter basket to move radially (i.e., to swing) about thelongitudinal axis A when the filter 1 is secured within the bloodvessel. The separation distance L₃ may range from no separation (i.e.,the first and second hubs 12, 14 are contiguous) to about 1 inch.Nominally, the separation distance L₃ is sufficient to permit the anchormembers 30 to deploy within the blood vessel and to provide sufficientflexibility for the filter basket 50 to swing the desired amount withinthe blood vessel. The connector 13 may be a single member, such as thickwire or tube, or a number of thin wires. The connector 13 can beconstructed of a variety of biocompatible materials, including but notlimited to stainless steel, Elgiloy®, or Nitinol. In an embodiment, thefilter 1 is delivered by pushing it through a catheter with a push rodwhich presses on the second hub 14. In this embodiment, the connector 13is sized to transmit the pushing force applied by the push rod from thesecond hub 14 to the first hub 12 without buckling. The connector 13 isalso sized to withstand, without buckling, the force applied by bloodflow through the vessel in the situation where the filter basket 50fills and maximum blood pressure is assumed at or near the filtrationsite. For example, referring to equations 1-6, the connector 13 of afilter intended for placement in an adult vena cava should be configuredto resist at least 418.7 grams in compression without buckling.

In the embodiment illustrated in FIGS. 1-13, the purpose andconfiguration of the second hub 14 is similar to that of the first hub12. Specifically, the second hub 14 connects the filter members togetherat their proximal ends by any of a number of suitable connectiontechniques, such as, for example, welding, laser welding, or plasmawelding, or being bonded together. The second hub 14 may be hollow orhave an interior space into which the proximal ends of the filtermembers may be inserted prior to brazing, welding (preferably by plasmawelding) or gluing with a biocompatible adhesive.

In the embodiment of the filter basket 50 illustrated in FIGS. 1-7, thebasket is formed by filter members that include a first segment 51, asecond segment 52 and a retainer member 55. According to thisembodiment, as shown in FIG. 2, the first segment 51 of each filtermember is preferably coupled (e.g., by brazing, welding or gluing) tothe second hub 14 on a proximal end and to the second segment 52 on itsdistal end in a joint or bend 53. The second segment 52 is furthercoupled to the retainer member 55 by joint 54. The retainer member 55connects to each of the distal ends of the second segments 52, asillustrated in FIG. 3A.

In this embodiment, the first segments 51 of the filter basket memberextend radially outward from the second hub 14 at an angle θ₃ from thelongitudinal axis A with a length L₄. The first segments 51 thereforegenerally define the bottom, with respect to blood flow, of the filterbasket 50 and provide the filter members for capturing emboli flowinginto the basket. In designing a filter for a particular blood vessel,the angle θ₃ and length L₄ of the first segments 51 are selected so thatthe diameter DF of the filter basket 50 is less than the internaldiameter of the blood vessel. In a preferred embodiment, angle θ₃ rangesfrom approximately 90 degrees to approximately 20 degrees, and morepreferably between approximately 80 degrees and approximately 45degrees, and the length L₄ ranges from approximately 0.2 inches toapproximately 0.6 inches.

In this embodiment, the second segments 52 of the filter members have alength L₅ preferably extending generally parallel to the longitudinalaxis A. In alternative embodiments, the second segments 52 may beoriented at an orthogonal angle to the longitudinal axis, so the filterbasket 50 forms a frustum. At their distal ends (i.e., upstream withrespect to blood flow), the second segments are coupled to the retainermember 55 by any suitable connection, including welding, brazing, gluingand/or wrapping the second segments 52 around the retainer member 55.The second segments of the filter basket 50 define the volume of thefilter basket for retaining emboli. Thus, the filter basket can bedesigned to capture and retain more emboli by increasing the length L₅of the second segments 52, without changing the anchor member 30configurations (which could impact their ability to engage the bloodvessel wall).

The retainer member 55 provides circumferential restraint to the secondsegments 52, thereby preventing radial expansion of the filter memberswhen the filter basket 50 fills with emboli. Additionally, in theembodiment illustrated in FIGS. 2, 3A and 3B, portions of the retainermember 55 extend radially outward from the longitudinal axis beyond thecircumference of the second segments 52 to form positioning pads 56.Referring to FIGS. 3A and 3B, the retainer member 55 extends at anoblique angle to the longitudinal access and radially outward to formthe positioning pads 56 spanning positioning diameter DP, which may beset to be approximately equal to the internal diameter of the bloodvessel. The positioning pads 56 may be provided with a suitableretention member such as, for example, the hook 40 shown and describedherein.

Viewed end on, the retainer member 55 has a star shape as illustrated inFIG. 3A. By extending further from the filter longitudinal axis than therest of the filter basket 50 (i.e., diameter DP defined by thepositioning pads 56 is greater that the diameter DF of the filter basket50), the positioning pads 56 may contact the vessel wall to position thefilter basket within the blood vessel. In the embodiment illustrated inFIGS. 1-7, the retainer member 55 preferably includes of a series oftriangles, which may be formed by laser cutting a hollow tube or bendinga single wire in the shape illustrated. But other forms are possible,including sine wave, interconnected or alternating arcs or alternatingsemicircles.

According to this embodiment, if blood pressure on emboli entrapped inthe filter basket 50 applies a radial force against the second segments52, this force is applied to the retainer member 55 at the joints 54. Tothe extent the retainer member 55 flexes under this force, the joints 54will be pressed radially outward which will draw the positioning pads 56radially inward (i.e., toward the longitudinal axis). Alternatively, theretainer member 55 may permit the filter basket 50 to expand radiallyoutward slightly but sufficiently restrain the expansion so that thefilter members do not press against the blood vessel wall. So if thefilter basket 50 fills with emboli and blood flow through the filter 1acts on the trapped emboli to produce a radial force that tends toexpand the filter basket, the positioning pads 56 will not transfer thisforce to the vessel wall, and may actually pull back from the vesselwall.

In addition to the advantage of preventing a full filter from applyinggreater pressure to the vessel wall, this retainer member 55 embodimentprovides blood flow paths around the filter basket, such as the areabetween adjacent positioning pads 56 and the circumference of the filterbasket 50, that remain open even if the filter basket is filled withemboli. Moreover, since the filter basket opening is upstream from theanchor members 30, the filter basket removes emboli from the bloodbefore they reach the anchor members where they might otherwise becaptured and increase the pressure applied to the anchor members.

Referring to FIG. 5, the alternating triangle form of the retainermember 55 also facilitates folding of the filter basket during assemblyso the filter can be fit into a catheter. As illustrated, the retainermember 55 will bend at each corner in an accordion fashion tosignificantly reduce its circumference and the positioning pads 56 canbe bent inward. Preferably, the retainer member 55 is fabricated from ashape memory alloy, such as Nitinol. The memory shape of a retainermember according to this embodiment is preferably the expandedconfiguration I, as shown in FIG. 5. The retainer member can then becooled and folded into its compressed configuration II for installationin a storage tube or catheter, as is also shown in FIG. 5. By folding inan accordion fashion, the retainer member 55 allows the filter basket tocollapse into the narrow profile of FIG. 6 for positioning within astorage tube or catheter.

Although the embodiment illustrated in FIGS. 1-3B features five filtermembers, more may be employed to reduce the space between filter membersin order to capture smaller emboli and/or to provide a larger filterbasket 50 for use in a larger blood vessel. For example, FIGS. 3A and 3Billustrate an embodiment including eight filter members. A filteraccording to the embodiment may also have fewer than five filtermembers. Other features of the filter basket 50 may be consistent withthose of the aforementioned embodiments.

While the aforementioned embodiments include a single retainer member55, additional retainer members may be used to provide more filter meshelements for capturing emboli and/or additional lateral restraint toprevent expansion of the filter basket 50. For example, FIG. 7illustrates an embodiment featuring three radial restraints, includingretainer member 55A at the upstream end, retainer member 55B at anintermediate position, and retainer member 55C at or near the downstreamend of the second segment 52.

Another embodiment of the filter basket 50 is illustrated in FIG. 8. Inthis embodiment, the filter members 58 first extend radially outwardfrom the second hub 14 so as to preferably bend through a radius R₂ incurved portion 58C to a linear portion 58L that is preferablyapproximately parallel to the longitudinal axis. Linear portion 58Lcouples to a retainer member 57 and bends radially outward to end in apad portion 58P. The pad portion 58P, by extending radially outward fromthe filter basket 50, may contact the blood vessel wall to position thebasket near the centerline of the vessel. A smooth portion forcontacting the blood vessel wall can be provided on the pad portion 58Pby bending the member through a tight radius R₃ so that the tip 58Tpoints inward toward the longitudinal axis. Not all filter members 58need to include a pad portion 58P, since the centering function may beaccomplished by as few as three, preferably equiangularly spaced padportions 58P. Radial expansion of the filter members 58 due to pressurefrom captured emboli will not result in increased pressure on the bloodvessel wall because the retainer member 57 prevents the pad portions 58Pfrom moving outwardly. This embodiment of the filter basket 50 resemblesa birdcage in its deployed configuration.

In order to fit the birdcage filter basket 50 embodiment into acatheter, the curved portion 58C and pad portions 58P of the filtermembers 58 are straightened and the retainer member 57 folds into areduced circumference, such as by folding accordion style as illustratedin FIG. 9.

In an embodiment of the birdcage filter basket, multiple retainermembers 57 may be employed, such as the three retainers 57A-57Cillustrated in FIG. 10. In order to fit this embodiment into a catheter,each of the retainer members 57A-57C fold into a reduced circumference,such as by folding accordion style as illustrated in FIG. 11.

An alternative embodiment of the birdcage filter basket 50 may be formedby employing a retainer member 55, such as illustrated in FIG. 5, whichincludes positioning pads 56 that are preferably pointed and extendradially beyond the diameter of the filter basket. With the positioningpads 56 able to center the filter basket 50 in the blood vessel, the padportions 58P of the filter members 58, such as are shown in FIGS. 8 and10, may be eliminated in this embodiment.

Yet another embodiment of a filter basket 50 is illustrated in FIG. 12A.In this embodiment, the filter members 59 are formed in a helical shape.The proximal ends of the filter members 59 are coupled to the second hub14 and the distal ends are formed into a pad portion 59P. For clarity,FIG. 12A shows only a single helical member 59, but more helical members59 may be used. For example, FIG. 12B shows a three-member filter basket50 from view D-D. But even more members 59 may be employed. Whenmultiple helical members 59 are employed, they are oriented on thesecond hub 14 equiangularly about the longitudinal axis in order topresent a tight mesh of filter members 59. For example, FIG. 12B showsthree members 59 spaced 120 degrees apart about the longitudinal axis.

The pad portion 59P on the distal end of each filter member 59 is formedby first bending the member radially outward away from the longitudinalaxis (as shown in FIG. 12B) and then back toward the longitudinal axis(as shown in FIG. 12A). By extending beyond the diameter of the filterbasket 50, the pad portion 59P may contact the blood vessel wall inorder to position the basket near the vessel's centerline.

In order to fit the helical embodiment into a catheter, the filtermembers 59 can be straightened and/or wound more tightly into a longer,tighter helix. Once the filter warms to body temperature, the filtermembers 59 will resume the helical form as illustrated in FIG. 12A.

Due to their helical shape, pressure on the filter members 59 byentrapped emboli does not lead to increased stress on the blood vesselwalls. As illustrated in FIG. 13, pressure on the emboli 5 from bloodflow 8 will be transferred primarily toward the second hub 14 via alongitudinal force component F₁. To the extent there is a radial forcecomponent F₂, this force is accommodated by the helical members 59expanding their diameters while contracting in length parallel to thelongitudinal access. Thus, there is no lever mechanism applyingadditional pressure to the blood vessel wall.

While the foregoing embodiments include a second hub 14 and an inter-hubconnector 13, these structures are not essential to providing a filterbasket that will not apply additional pressure to the blood vessel wallor block blood flow when filled with emboli. For example, FIG. 14illustrates an embodiment which replaces these structures by extendingthe filter members with an extended section 61. In this embodiment, theextended section 61 separates the filter sections 51, 52 of the filtermembers from the hub 12 and anchor members 30. Each filter basketextended section 61 is coupled to the first section 51 by a bend or weldand extends generally parallel to the longitudinal axis for a length L₆to its proximal end. The proximal end of the extended sections 61 may beinserted into and coupled to (e.g., by welding, brazing or gluing) thehub 12 to hold the ends together. The length L₆ of the extended sections61 may be sufficient to place the filter basket 50 upstream (withrespect to blood flow) from the anchor members 30 to help facilitatedeployment of the filter in the blood vessel without the filter andanchor members becoming tangled. Additionally, the length of theextended section 61 gives it flexibility so the basket can move (i.e.,swing) within the blood vessel to allow the filter basket to seek theblood vessel centerline and avoid applying undue pressure to a point orportion of the blood vessel wall. The embodiment of FIG. 14 can beprovided with anchor members (not shown) coupled to the distal end ofthe basket 50 proximate the pad points 56. The feature of anchor membersconnected to the pad points 56 is believed to alleviate pressure appliedagainst the hub 12 as long as such anchor members do not expand radiallyoutward.

In the embodiments illustrated in FIG. 14, pressure applied by embolicaptured in the filter basket may cause the extended sections 61 toexpand radially. But this movement will not result in greater pressurebeing applied to the blood vessel wall because the retainer member 55prevents expansion of the distal end of the filter member 52. Thus,additional retainer members are not required with this embodiment.Nevertheless, this embodiment may be combined with the multiple-retainerembodiments illustrated in FIGS. 7 and 10. Also, in an alternativeembodiment, the extended sections 61 may be held together by a band 62positioned a distance from the hub 12, such as in the vicinity of thebend joining the extended sections 61 with the first sections 51. Theband 62 may be any bio-compatible material and may be joined to theextended sections 61 by welding, brazing, or gluing. Alternatively, theband 62 may not be a separate piece, and instead may be formed bywelding, brazing or gluing the extended sections 61 together.

In the embodiment illustrated in FIG. 14, the filter members and filterbasket may be constructed using any of the techniques described abovewith respect to the foregoing embodiments. So the filter basket mayinclude more filter members as illustrated in FIGS. 4A and 4B, or be oneof the birdcage embodiments illustrated in FIGS. 8-11. The helicalfilter basket embodiment illustrated in FIGS. 12A and 12B may also beemployed, particularly in combination with a band 62 positioned abovethe start of the helical form to hold the helixes in longitudinalalignment.

FIG. 14 also illustrates an embodiment of a hollow hub 12. In thisembodiment, the first anchor segments 31 and extended filter members 61are inserted into the hollow hub 12 for bonding. In this embodiment, thehub 12 provides lateral support for the first anchor segments andextended filter member sections 31, 61. This may permit the filtermembers to experience greater bending force than embodiments in whichthe members are welded to an end surface of the hub, which isadvantageous for embodiments that feature filter members, like theextended filter sections 61 that are subject to bending in service. Thisembodiment enables a number of assembly alternatives. The first anchorsegments and extended filter member sections 31, 61 may be weldedtogether and then covered by and bonded to the hub 12. Alternatively,these components 31, 61 may be first inserted into the hub 12 and thenwelded to each other and to the hub. Alternatively, the components 31,61 may be first inserted into the hub 12 and then brazed together and tothe hub. Alternatively, the components 31, 61 may be first inserted intothe hub 12 and then glued together and to the hub with a bio-compatibleadhesive.

The various embodiments feature a filter basket 50 that is positionedupstream with respect to blood flow 8 from the anchor members and thatdoes not include hooks or other anchoring structure. Thus, the filterbasket floats in the blood vessel upstream from the anchoring structure.Radial positioning structures, such as generally pointed positioningpads 56, and/or generally curved pad portions 58P, 59P help the filterto locate (float) near the centerline of the blood vessel withoutapplying undue stress to the walls. This configuration permits thefilter basket to capture emboli without applying additional pressure tothe blood vessel walls when the filter fills with emboli.

The use of a thermal shape memory material, such as Nitinol, for theanchor and filter members facilitates collapsing the filter radiallyinward from its normally expanded (i.e., unconstrained) configurationinto a more compact configuration for insertion into a blood vessel.

By forming the anchor and filter members from a shape memory material orNitinol alloy material, such as Nitinol wire, transition between themartensitic and austenitic forms of the material can be achieved bytemperature changes above and below a transition temperature (referredto herein as the martensitic-to-austenitic transition temperature).

Using a shape memory material, such as Nitinol, the deployed shapes andconfigurations of the filter members can be set (i.e., imprinted with amemory shape) by annealing the members at high temperature while holdingthem in the desired shape. Thereafter, whenever the filter is in theaustenitic form (i.e., at a temperature above themartensitic-to-austenitic transition temperature), the members return tothe desired shape. Example methods for setting the high-temperatureshape of filters are disclosed in U.S. Pat. No. 4,425,908, which ishereby incorporated by reference in its entirety.

By virtue of the characteristics of shape memory material, the anchorand filter members can be held in a collapsed, straight form that canpass through a length of fine plastic tubing with an internal diameterof approximately two millimeters (2 mm), e.g., a No. 7 French internaldiameter catheter. In its high temperature form, the filter 10 recoversto a preformed filtering shape as illustrated in FIGS. 1, 2, 3B, 4B, 7,8, 10, 12, 13, and 14. Alternatively, the anchor and/or filter membersmay be made of spring metal wires which can be straightened andcompressed within a catheter or tube and will diverge into the filtershapes illustrated in the figures when the filter is ejected from adelivery catheter.

FIG. 15 illustrates another embodiment of a filter which includes asecond filter basket 50′ positioned upstream from the first filterbasket 50. The structure of the second connector 13′ and second hub 14′are similar to those for the first connector 13 and first hub 14described above. Further, the second filter basket 50′ preferablyincludes filter elements 51′, 52′ and 56′ which are preferably similarto those for the first filter basket 50 described above. The secondfilter basket 50′ may be sized to be smaller in cross section than thatof the first filter basket 50 so that the filtering of emboli is dividedbetween the two filter baskets 50, 50′. In the second filter basket 50′,the number of filter members 51′ and 52′ can be configured to providefor an open area ratio larger than an open area ratio of the firstfilter basket 50 so that blood clots that pass through the second basket(which has a larger open area ratio) are captured downstream by thefirst filter basket 50 (which has a smaller open area ratio). In thepreferred embodiment, the open area ratio of the second filter basket50′ can be at least 20:1 while the open area ratio of the first basketcan be at least 10:1. Hub 12 to which anchor members 30 are coupled mayalternatively be placed between the first and second filter baskets, asis shown in FIG. 15A.

In another embodiment, the filter baskets may be formed from sheets ofmetal alloy or tubular stock, such as Nitinol, or plastic perforatedwith numerous holes. The holes in the sheets are sized and spaced tocapture emboli and provide enough flow through the filter to prevent theformation of emboli and ensure sufficient filtering of the blood. Inthis embodiment, the sheets are joined along longitudinal folds so thefilter sheets can be collapsed to a narrow profile for positioningwithin a catheter.

A filter 1 according to the various embodiments may be delivered to ablood vessel by a delivery unit such as, for example, the unit describedin U.S. Pat. No. 6,258,026, which is incorporated by reference in itsentirety. The filter 1 is delivered through a catheter or delivery tubeto a generally centered position within a body vessel, as described infurther detail in the above-mentioned patent. Further methods ofdelivering a blood filter suitable for use with the various embodimentsare disclosed in PCT International Application No. PCT/US06/17890,entitled “Embolus Blood Clot Filter and Delivery System,” filed on May9, 2006, which is hereby incorporated by reference in its entirety.

While the present invention has been disclosed with reference to certainpreferred embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the present invention. Accordingly, it is intendedthat the present invention not be limited to the described embodiments,but that it have the full scope defined by the language of the followingclaims, and equivalents thereof.

1-26. (canceled)
 27. A filter to be placed in a flow of blood through ablood vessel having a blood vessel wall, the filter comprising: a) afilter body that comprises one or more helical members surrounding aninterior basket area and having an initial diameter, the body havingfirst and second end portions and a first length in between said endportions; b) one or more pads on the second end portion of each of thehelical members, each pad extending a distance radially away from thehelical member initial diameter, each pad positioned to engage the bloodvessel wall; c) the body being expandable to an expanded position of asecond diameter responsive to a filling of the interior basket withemboli, wherein said second diameter is larger than the first diameterand wherein said body length is shortened to a second smaller lengththat is smaller than the said first length in said expanded position.28. The filter of claim 27, wherein one or more of the pads have hooks.29. The filter of claim 27, wherein there are multiple of said helicalmembers, each having a said pad.
 30. The filter of claim 29, wherein thehelical members are equi-angularly spaced apart.
 31. The filter of claim27 further comprising a head with a diameter that is smaller than saidinitial diameter, each said helical member attached to said head. 32.The filter of claim 27, wherein each helical member is a wire.
 33. Thefilter of claim 32 wherein each pad is a part of said wire.
 34. Thefilter of claim 32 wherein the said wire has a free end portion.
 35. Thefilter of claim 34 wherein the pad is a part of said wire free endportion.
 36. A filter to be placed in a flow of blood through a bloodvessel, the filter comprising: a) a hub deposed along a longitudinalaxis; b) one or more helical members joined to the hub; c) the helicalmember or members defining a filter basket having an initial diameter, afilter basket interior and a filter basket opening, the filter basketconfigured so that the filter basket's opening faces away from the hub;d) wherein the basket opening is receptive of emboli that expand thebasket once the basket interior collects a plurality of emboli.
 37. Thefilter according to claim 36 wherein each helical member is a wire. 38.The filter according to claim 37, wherein each of the wires has a padthat extends beyond said initial diameter.
 39. A filter to be placed ina flow of blood through a blood vessel having a blood vessel wall, thefilter comprising: a) a hub disposed along a longitudinal axis; b) aplurality of equi-angularly spaced apart helical members projecting fromthe hub, at least some of the plurality of helical members including apad configured to engage the wall of the blood vessel when the filter ispositioned in the blood vessel and expanded to an expanded diameter; c)the helical members defining a filter basket having a basket peripheryof an initial diameter that surrounds a basket opening into which bloodcan flow to generate said expanded diameter to a larger diameter. 40.The filter of claim 39 wherein each said pad has a hook.
 41. The filterof claim 39 wherein each helical member is a wire.
 42. The filter ofclaim 39 wherein the hub has a diameter that is much smaller than thesaid initial diameter.
 43. The filter of claim 39 wherein each helicalmember has first and second end portions, the first end portion attachedto the hub, the second end portion being a free end portion and whereineach helical member forms a part of said basket with said hub.
 44. Thefilter of claim 43 wherein said basket has a smaller tapered portionnext to the hub.
 45. The filter of claim 39 wherein each helical memberextends around said longitudinal axis at least 180 degrees.
 46. Thefilter of claim 39 wherein each helical member extends around saidlongitudinal axis at least 270 degrees.
 47. The filter of claim 39wherein each helical member extends around said longitudinal axis atleast 360 degrees.
 48. The filter of claim 39 wherein the hub and thehelical members are of differing materials.
 49. The filter of claim 48wherein the helical members are of a metallic material.
 50. The filterof claim 48 wherein the hub is of a non-metallic material.